1. Field of The Invention
The invention relates to a method and apparatus for grouting an offshore structure such as a platform for use in conjunction with the drilling and production of a subterranean well.
2. Description of the Prior Art
Various types of grouting procedures for the annular space between the jacket and piling for offshore structures have been heretofore provided. The patent to Manning, U.S. Pat. No. 3,213,629 discloses a method of installing a pile wherein the pile is positioned within the jacket and thereafter the pile is hammered into the sea bed to such an extent that the upper end of the pile is below the top of the jacket and the surface of the water, and the hammer follows the pile downwardly within the jacket. While the pile is being driven, the water level within the jacket is lowered at a rate which maintains the water level below the lower face of the hammer. Thereafter, the grouting procedure is initiated.
The patent to Harris, U.S. Pat. No. 3,468,132 discloses a packer assembly for sealing an annular area between pilings and skirt guides for insertion of the piling, the guides being located at the bottom of platforms and secured by means of the piling to the floor of the sea. The annular area between the guides and the piling is filled with grout above the packer assembly after setting of the packer upon completion of driving of the piles.
The patent to Thaxton, U.S. Pat. No. 3,570,259 entitled "Annulus Seal and Pile Wiper" discloses a seal for sealing the annulus between a pile and a platform leg for subsequent cementing or grouting.
The patent to Olsen, et al., U.S. Pat. No. 3,601,999 teaches the use of compressed air which is introduced into an annular area between the platform jacket and the piling so that water can be expelled from the annular area through the lower end of the platform jacket or sleeve for subsequent introduction of a grouting material. The introduction of compressed air and grouting material is effected from above the water line, thus avoiding any necessity of having to perform the grouting step by utilizing divers.
The patent to Bassett, U.S. Pat. No. 3,811,289 discloses the use of a predetermined amount of grout for introduction from the top into the annular area between the piling and a leg sleeve or jacket. The amount of material is calculated to be sufficient to displace water from the space through the lower end of the jacket. Upon setting, the grout forms a plug in the bottom portion of the annular area. Additional grout then is introduced to fill the upper portion of the annular space and is allowed to set.
The patent to Bassett, et al., U.S. Pat. No. 3,832,857 discloses a method for grouting the annular area between the jacket and the platform leg which utilizes air introduced into the annular area to expel water from the lower end of the annular area. Thereafter, the annulus is filled from the top with the grouting material. Water may be pumped down the annular area to wash out any mud. Additionally, a minor amount of grouting material may be pushed out the bottom of the annular area to remove mud or to form a bell shaped foundation.
The strength of a cement-like material, such as grout, is the resistance which it offers to being crushed (which is defined as its compressive strength) or pulled apart (which is defined as its tensil strength). These two types of strengths are, of course, related, with compressive strength generally ranging from about 5 to about 10 times higher than the tensil strength of given samples of set cement.
Normally, the testing of the compressive strength of cement is conducted under very strict, uniform requirements. Cubes of cement slurry generally are allowed to set and cure under a water blanket, either at atmospheric pressure or at a specified pressure, usually up to, but no more than, about 3000 p.s.i. Cement cured under pressure generally will have a higher compressive strength than a similar sample which has been cured only at atmospheric pressure.
The coefficient of friction between surfaces is the ratio of the force required to move one surface over the other surface in relation to the total force compressing the two surfaces together. Thus, if "F" is the force which is required to move one surface over another, and "W" is the force pressing the surfaces together, the coefficient of friction may be defined by the formula: K = F/W.
The coefficient between two samples of grout, one over the other, is approximately 1.8 times the coefficient of friction between steel and a similar section of grout. Therefore, if the plane of shear between a piling and a piling sleeve, which is normally steel on grout, can be shifted to produce a shear plain of grout on grout, then the force necessary to shift the piling either in or out of the piling sleeve is greatly enhanced.
Utilizing prior art grouting methods, the configuration of piling with respect to the piling sleeve, where no pressure has been applied to the grout, is as shown in FIG. 6. Here, the plane of shear is between the grout and steel as indicated by lines A--A and B--B. However, by utilizing the method of the present invention, pressurizing the annular area between the piling and the sleeve will cause the sleeve to flex in an outward position and the piling to flex in an inward position. As a result, two beneficial effects are obtained. First, a greater volume of grout may be placed within the annular area which shifts the plane of shear to A'--A' and B'--B' as shown in FIG. 7. As a result of this first beneficial effect, the plane of shear is now grout on grout, as opposed to grout on steel. Accordingly, the shear out characteristics of the piling have been greatly increased, in addition to providing greater stability between the piling and the piling sleeve. The ultimate result is a more stable and safe platform structure.
It is an object of the present invention to seal off the upper and lower end of a sleeve which surrounds a piling and then filling the space between the jacket and the piling with grouting material.
Another object of the present invention is to close off the upper and lower end of the sleeve surrounding the piling by utilizing expanding inflatable seal means to seal off the space therebetween, thereafter filling the space with grouting material and maintaining a pressure greater than the static head pressure exerted by the grout column and water column at the grouting depth on the grouting material in the space until it has set.
A further object of the invention is to fill the annular space between a piling and a surrounding jacket or sleeve by providing seal means adjacent the upper and lower end of the jacket, providing inflating fluid to the seal means to maintain the space closed off and thereafter injecting grouting material into the space while retaining the inflating pressure trapped in the seal means.
Yet a further object of the invention is to fill the annular space between a piling and a surrounding jacket or sleeve by providing expandable seal means adjacent the upper and lower end of the jacket, providing inflating fluid to the seal means to inflate the seal means to maintain the space closed off and thereafter injecting grouting material into the space while retaining the inflating pressure trapped in the expanded seal means and maintaining a pressure greater than the static head pressure exerted by the grout column and water column at the grouting depth on the grouting in the space until the grout has taken a permanent set.
Still a further object of the present invention is to provide a method of grouting the annular area between the piling and a platform sleeve whereby the coefficient of friction is transferred from grout on steel to grout on grout.